Through examples discovered in the sections on acids and bases proton-transfer procedures are broken into two theoretical steps: (1) donation of a proton by an acid, and also (2) acceptance of a proton by a base. (Water served as the basic in the mountain example and as the acid in the base example ). The theoretical steps room useful since they make it straightforward to view what varieties is left after ~ an mountain donated a proton and also what varieties is formed when a base embraced a proton. We shall use hypothetical steps or half-equations in this section, yet you need to bear in mental that totally free protons never actually exist in aqueous solution.

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Suppose we first consider a weak acid, the ammonium ion. Once it donates a proton to any kind of other species, we deserve to write the half-equation:

\< \textNH_4^+ \rightarrow \textH^+ +\textNH_3\>

The submicroscopic representations below show the donation the the proton of ammonium. The removal of this proton results in NH3, which is easily seen in ~ the submicroscopic level.

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But NH3 is just one of the link we recognize as a weak base. In various other words, when it donates a proton, the weak mountain NH4+ is transformed into a weak base NH3. One more example, this time beginning with a weak base, is provided by fluoride ion:

\<\textF^- + \textH^+ \rightarrow \textHF\>

The submicroscopic representation over shows just how the enhancement of a proton to fluoride switch a weak base (F- in green) into a weak acid (HF).

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The case just described for NH4+ and also NH3 or for F– and also HF uses to all acids and bases. Anytime an acid donates a proton, the acid changes into a base, and also whenever a basic accepts a proton, an acid is formed. One acid and also a basic which differ only by the presence or absence of a proton are dubbed a conjugate acid-base pair. Therefore NH3 is referred to as the conjugate base of NH4+, and NH4+ is the conjugate acid of NH3. Similarly, HF is the conjugate acid of F–, and F– the conjugate basic of HF.


The usage of conjugate acid-base pairs allows us to make a very straightforward statement around relative strengths of acids and also bases. The more powerful an acid, the weaker that conjugate base, and, vice versa, the stronger a base, the weaker its conjugate acid.

TABLE \(\PageIndex1\):Important Conjugate Acid-Base Pairs.

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